In Cubase, go to Devices, select Device Setup and then select VST Audiobay. In VST Audiobay, make sure that you have the MI4 driver selected and not Built In Audio. Once you have the proper driver selected, go to VST Connections, select the Outputs tab and set the left and right outputs to the MI4 outputs.

If there is no MI4 option to select in VST Audiobay, go to the download section at www.steinberg.net and download the latest driver update for the MI4 for the MAC. Once the driver is installed, you will be able to select the MI4 as the default ASIO driver in Cubase.